Clay based catalytic process for the preparation of acylated aromatic ethers

ABSTRACT

This invention relates to a process for the preparation of acylated aromatic ethers, in particular the acylation of anisole (methoxybenzene) and veratrole (1,2-dimethoxybenzene) for the preparation of corresponding acylated aromatic ether, namely, p-methoxyacetophenone and 3,4-dimethoxyacetophenone respectively, using clay based heterogeneous catalysts, and their lanthanide exchanged forms at moderate temperature and pressure with high selectivity.

FIELD OF THE INVENTION

The present invention relates to a clay based catalytic process for thepreparation of acylated aromatic ethers. More particularly, the presentinvention relates to the catalyzed acylation of anisole (methoxybenzene)and veratrole (1,2- dimethoxybenzene) for the preparation of acylatedaromatic ether, namely, p-methoxyacetophenone and3,4-dimethoxyacetophenone respectively, using a series of lantanidecation exchanged clay based catalysts.

BACKGROUND OF THE INVENTION

Acylated aromatic ethers are of commercial importance in fine chemicalsindustries, as many synthetic fragrances and pharmaceuticals contains anacyl group, and these ethers are useful intermediates. Acylated anisoleis used for synthesis of 2-(4-Methoxybenzoyl) benzoic acid, the sodiumsalt of which is used as sweetening agent. Similarly, acylated veratroleis a synthon for preparation of vesnarinone1-(3,4-Dimethoxybenzoyl)-4(1,2,3,4-tetrahydro-2-oxo-6-quinolinyl)piperazine which is a cardiotonic drug.

Reference is made to U.S. Pat. No. 62747441 B1 (Aug. 14, 2001, B. M.Choudary et al.) wherein it is disclosed that acylation of heteroaromticcompounds like furan, thiophene, or pyrrole with the anhydride of C₂₋₅carboxylic acid (e.g. acetic anhydride) was carried out using Fe⁺³exchanged Montmorillonite clay. The reaction was carried out in thetemperature range of 0 to 130° C. for 1 to 24 hours and the2-acylaromatic compound was separated by conventional methods to obtain2-acetylpyrrole of high purity. The drawback of this process is thelonger reaction time and high temperature.

Reference is made to the work of B. M. Choudary et al, Applied CatalysisA, General 171 (1998) 155-160 which describes the acylation of aromaticethers with acid anhydrides in the presence of cation exchanged claysviz., Fe⁺³ and Zn⁺² exchanged montmorillonite clays. The reactionmixture of 46 millimoles of anisole and 10 millimoles of aceticanhydride and 250 mg of catalysts was stirred under nitrogen atmosphere.After 10 hours it gives conversion in the range of 25 to 70 percent. Thedrawback of this process is long reaction time, and the catalyst showsloss in activity. Reference is made to U.S. Pat. No. 5,637,773 (1993:Jean-Roger Desmurs et al.) wherein it is disclosed that 40 millimoles ofan aromatic substrates and 10 millimoles of acylating agents with excessamount of Bismuth halide as a catalyst, was mixed at room temperatureand then refluxed the reaction mixture for 6 hours to gives 67% of4-acylated anisole. The drawback of this process is that more thanstochiometric amounts of bismuth chloride was used and also posesproblem of post-reaction catalysts separation. Furthermore, the Lewisacid must be eliminated from the reaction medium by carrying out acidicor basic hydrolysis at the end of the reaction.

Reference is made to German Patent DE 3809260 (1989, Botta A., et al.)wherein anisole and acetic anhydride were stirred for 3 hours withMordenite zeolite catalysts at 160° C. under 20 bar of nitrogen pressureto give 75% conversion with 98% selectivity for p-methoxyacetophenone.This process has disadvantage of operating at high temperature and veryhigh pressure and also needs a solvent for uniform mixing. Reference ismade to Japanese Patent 1993-317557 (19931217. C. A.124;8397 Myata,Akira et al.) wherein a mixture of veratrole and propionyl chloride, inthe presence of Zeolite-β was refluxed for three hours to give ca, 70%of 3,4-dimethoxypropiophenone. The drawback of the process is that ituses propionyl chloride as an acylating agent, which generates toxichydrochloric acid during acylation reaction

Reference is made to the work of C. Kuroda et al, (Sei. Papers Inst.Phys. Chem. Res. 18, pp 51-60 (1932)) which describes the preparation ofmethoxyacetophenones by the reaction of an aromatic compound carryingmethoxy group with acetyl chloride in the presence of excess amount ofAlCl₃ to obtain high conversions. This process has disadvantages likemore than stochiometric amounts of aluminum chloride due to complexationwith the ketone formed and also involved process of post reactioneffluent treatment and use of corrosive and irritant AlCl₃. The majordrawback of the above stated process is separation of catalysts aftercompletion of the reaction. This necessitates a long, expensivetreatment following hydrolysis, extraction of the organic phase,separation of organic and aqueous phase and even drying of latter.Further, there are problems with aqueous saline effluent which has to beneutralized and which necessities additional operation. The Lewis acidcannot be recycled, as it has been hydrolyzed.

Reference is made to the work of H. Burton and P. F. G. Praill (Journalof Chemical Society, April-1950, pp-1203-1206) wherein it is reportedthat Acetyl perchlorate formed in-situ from silver perchlorates andacetyl chloride, is an effective acylating agent and will convertanisole into p-methoxyacetophenone in about 70% yield. However, thisprocess has disadvantages of using perchlorates which is hazardouschemical. Reference is made to the work of E. J, Bourne, et al. (Journalof Chemical Society, March-1951, pp-718-720) wherein trifluoroaceticanhydride catalyst is shown to promote, the condensation betweensuitably activated aromatic compound and carboxylic acid or sulphonicacid to give ketones or sulphones, respectively. In this process,reaction was done at room temperature. Anisole was added to a mixture oftrifluroacetic anhydride and acetic acid. After three hours the solutionwas poured into the excess of sodium hydrogen carbonate solution andthen extracted by chloroform The extract were dried, filtered andevaporated to dry syrup. After crystallization it gave 78% ofp-methoxyacetophenone.

The reported process is multi-step process wherein separation of theproduct with very high recovery is a limitation.

Reference is made to the work of Cullinane N. M. et al. (Journal ofChemical Society, Feb-952, pp-376-380) wherein acylation of benzene,toluene and anisole is reported using TiCl₄ as a catalyst. Acids, acidchlorides and anhydrides were used as the acylating agents. Acid isreported to be the least and anhydride the most effective towards theformation of acylated products. With anisole (0.15 g-mols) and aceticanhydride (0.1 g-mol) and titanium tetrachloride (0.22 g-mol), the yieldof p-acylated product was reported 76% after 4 hours. With anisole (0.2g-mols) and benzoic acid (0.2 g-mols) and titanium tetrachloride (0.4g-mols) the yield of p-acylated product was 63% after 1.5 hours. Theprocess has disadvantage of separation of product, as it requires morethan one step, like hydrolysis, separation of organic layer and finallyremoval of solvent at reduced pressure.

OBJECTS OF THE INVENTION

The main object of the present invention is to provide clay basedcatalytic process for the preparation of acylated aromatic ethers, whichobviates the drawbacks as detailed above.

Another object of the invention is to develop clay based acylationprocess for aromatic ethers, which operates at moderate conditions ofpressure, temperature and without the requirement of any solvent andyields high conversions for veratrole and for anisole.

Another object of the invention is to provide a process using solid acidheterogeneous catalysts, which are environmentally friendly, safe inhandling and the acylating agent does not generate any hazardousbyproduct.

Another object of the invention is to provide a process whereinacylation of aromatic ether occurs selectively at para position.

Another object of the invention is to provide a process where acylationof aromatic ether is carried out catalytically with high atom efficiencywithout giving rise to byproducts.

SUMMARY OF THE INVENTION

Accordingly the present invention provides a process for the preparationof an acylated aromatic ether which comprises acylating the aromaticether with an acylating agent in presence of a solid acid heterogeneouscatalyst comprising a rare earth cation exchanged clay based catalyst,separating the catalyst and the acylated aromatic ether obtained.

In one embodiment of the invention, the lanthanide cation exchanged claycatalyst is an upgraded smectite clay wherein the hydrogen ion isexchanged with a sodium ion.

In another embodiment of the invention, the hydrogen ion is exchangedwith a sodium ion using an acid selected from the group consisting ofHCl, HNO₃, and an organic acid.

In another embodiment of the invention, the rare earth ion is selectedfrom the group consisting of lanthanum, cerium, neodymium, praseodymiumand samarium.

In a further embodiment of the invention, the amount of rare earth ionin the catalyst is in the range of 5 to 10 weight % of the clay.

In a further embodiment of the invention, the rare earth ion is obtainedusing a soluble salt of the rare earth selected from the groupconsisting of nitrate, chloride and acetate.

In another embodiment of the invention, the acylation of the aromaticether is carried out in a single step under solvent free condition andat a temperature in the range of 80 to 120° C. and under atmosphericconditions without generating any by-product.

In a further embodiment of the invention, the acylation of the aromaticether is carried out at a temperature of 100° C.

In another embodiment of the invention, the acylating agent is selectedfrom the group consisting of a chloride and a carboxylic acid anhydride.

In another embodiment of the invention, the carboxylic acid anhydride isacetic acid anhydride or a homologue thereof.

In another embodiment of the invention, the catalyst is separated andrecycled.

In another embodiment of the invention, the aromatic ether is selectedfrom the group consisting of veratrole and anisole.

In another embodiment of the invention the process is solvent free withthe aromatic ether itself acting as the solvent.

In yet another embodiment of the invention the catalytic reaction iscarried Out in the range from 1 to 20 atmospheres.

In yet another embodiment of the present invention the ether to catalystratio is in the range of 1.3 to 1:5.

The invention also relates to a clay based catalytic process for thepreparation of an acylated aromatic ether which comprises (i) preparingupgraded smectite clay in the range of 0.5 to 5% weight percent; (ii)drying the clay in the temperature of 80 to 120° C. for 8 to 12 hours;(iii) exchanging hydrogen ion for sodium ion using a mineral acidselected from the group consisting of HCl and HNO3 or an organic acid;(iv) preparing Lanthanide exchanged clay using a soluble salt of alanthanide cation; (v) maintaining the ether to catalyst ratio in therange of 1 to 5; mixing the catalyst so prepared with the aromatic etherand an acylating agent and acylating the aromatic ether at a reactiontemperature in the range of 80 to 120° C. and time in the range of 1 to9 hours under solvent free reaction mixture at atmospheric pressure;(vi) separating the catalyst and the acylated product by distillation.

DETAILED DESCRIPTION OF THE INVENTION

In a typical procedure for the preparation of a clay based catalysts,the raw clay is upgraded by sedimentation to remove quartz, grits etcimpurities. Wet solid clay is separated from the clay slurry byultracentrifuge and naturally dried from 6 to 12 hours, followed bydrying at 80° C. to 120° C. for 4 to 8 hours. Thus dried clay wastreated with acid solution to convert the clay into H-form 10 gm of theclay thus prepared H-form of clay was refluxed with 100 ml of 0.01 Msolution of soluble salt like nitrate, chloride or acetate of relativelanthanide cations for 6 hours. Then catalysts was filtered washed withhot distilled water till the filtrate became anion free and driedovernight 110° C. for removing the moistures, clay was activated at 120°C. for 4-6 hrs before using for reactions. A typical chemical analysisof clay used for making catalysts was.

SiO2 Al₂O₃ R₂O₃ Na₂O K₂O MgO CaO LOI 52. 7.08% 31.43% 0.09% 0.33% 2.46%3.66% 6.14% 61%

The clays prepared were characterized for crystallinity by using X-raypowder diffraction using Philips X'perts MPD model and for BET surfacearea using Micromeritics ASAP-surface area analyzers.

Catalytic studies using above catalysts were done in continuous stirredtank reactor (CSTR) of 50 ml capacity having temperature controller,water circulator, magnetic stirrer and moisture trap. Typically, 5.5 gof veratrole (or 4.3 g of anisole) and 3.5 g of acetic anhydride weretaken in a 50 ml capacity round bottom flask to which 2 gm of thecatalyst after activation at 120° C. for 4 to 10 hours in muffle furnacewas added. The round bottom flask was fitted with a condenser throughwhich constant temperature water was circulated. Moisture trap wasattached at the end of the condenser. The contents of the flask wereconstantly stirred using a magnetic stirrer. The flask was kept in anoil bath whose temperature was slowly raised to desired reactiontemperature. The contents of the flask were analyzed by gaschromatography at different time intervals ranging from 1 to 8 hours.The yield was followed over time by taking aliquots which were analyzedby Gas Chromatography HP model 6890 using capillary column HP-5. Percentyield of p-acyl anisole or p-acyl veratrole was calculated usingfollowing equation

Percent Yield=number of moles of para acyl aromatic ether actuallyformed/number of moles of para acyl aromatic ether theoreticallyexpected,

In the present invention upgraded clay was exchanged with soluble saltof lanthanide cations like lanthanum cerium, neodymium, praseodymium,samarium ranging from 5 to 10 wt % of the clay to make them more activetowards acylation of anisole and veratrole. Further this improvedcatalytic process obviates the need of any solvent and the reaction canbe carried out at atmospheric pressure. The lanthanide cations in theinterlayer space of clays helps the catalytic conversion to be carriedout at moderate temperature.

The inventive steps adopted in this invention are: (i) Clays aremodified with rare earth in the range of 5 to 10 weight % to make thecatalysts more compatible with acylation reactions; (ii) the acylationreaction is carried out in single step so that the multi-step processcan be avoided; (iii) the lower temperature and pressure favors theselectivity for para position, which is desired; (iv) the catalyticreaction proceeds at relatively moderate temperature of 100° C. and atatmospheric pressure, which obviates the need of high temperature andpressure, (v) acylation occurs without use of any solvent and withoutusing hazardous and effluent generating acylating agent.

The following examples are given by way of illustration and thereforeshould not be construed to limit the scope of the present invention.

EXAMPLE 1

100 grams of raw clay was mixed with 10 liters of distilled water andthus formed slurry was thoroughly stirred at ambient temperature for 6hours. The slurry was then sedimented for 24 hours followed bydecantation of suspended clay solution. Upgraded solid clay wasrecovered first by natural drying followed by drying in oven at 110° C.for 6 hours. Thus crude clay was further refluxed with 2 normal solutionof sulfuric acid in a round bottom flask with a solid to liquid ratio1;5 at 80° C. for 2 hours. Clay was filtered and washed with distilledwater till it became free from sulphate ion as tested by barium sulphateand was finally dried at 110° C. for 6 hours. Thus obtained clay wastermed as H-clay. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 gms of H- Clay catalysts in abut 50ml capacity of round bottom flask kept in oil bath and the temperatureof oil bath was slowly raised to desired temperature of 100° C. Theround bottom flask provided with a water-circulator,temperature-controller, magnetic stirrer and moisture trap The contentsof the flask were analyzed by gas chromatography at different timeintervals ranging from 1 to 9 hours. The percent yield of p-acylveratrole and p-acyl anisole respectively shown in table 1a and 1b from31 to 77% and 12 to 41% were obtained.

EXAMPLE 2

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt (nitrate, chloride oracetate) of Lanthanum for 6 hours. Then the catalysts was filtered,washed with hot distilled water till the filtrated became anion free anddried overnight at 110° C. for removing the moisture Clay catalysts,La-clay thus obtained was activated at 120° C. for 4 to 6 hours beforeusing for reaction. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 grams catalyst in abut 50 mlcapacity of round bottom flask kept in oil bath and the temperature ofoil bath was slowly raised to desired temperature of 100° C. The roundbottom flask provided with a water-circulator, temperature-controller,magnetic stirrer and moisture trap. The contents of the flask wereanalyzed by gas chromatography at different time intervals ranging from1 to 5 hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b form 56 to 88% and 38 to 49% wereobtained.

EXAMPLE 3

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt (nitrate, chloride oracetate) of cerium for 6 hours. Then the catalysts was filtered, washedwith hot distilled water till the filtrated became anion free and driedovernight at 110° C. for removing the moisture. Clay catalysts, Ce-claythus obtained was activated at 120° C. for 4 to 6 hours before using forreaction. 40 milimoles of aromatic ether and 40 milimoles of aceticanhydride were reacted with 2 grams catalysts in abut 50 ml capacity ofround bottom flask kept in oil bath and the temperature of oil bath wasslowly raised to desired temperature of 100° C. The round bottom flaskprovided with a water-circulator, temperature-controller, magneticstirrer and moisture trap. The contents of the flask were analyzed bygas chromatography at different time intervals ranging from 1 to 5hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b from 57 to 91% and 35 to 52% wereobtained.

EXAMPLE 4

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt (nitrate, chloride oracetate) of neodymium for 6 hours. Then the catalysts was filtered,washed with hot distilled water till the filtrated became anion free anddried overnight at 110° C. for removing the moisture. Clay catalysts,La-clay thus obtained was activated at 120° C. for 4 to 6 hours beforeusing for reaction. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 grams catalysts in abut 50 mlcapacity of round bottom flask kept in oil bath and the temperature ofoil bath was slowly raised to desired temperature of 100° C. The roundbottom flask provided with a water-circulator, temperature-controller,magnetic stirrer and moisture trap. The contents of the flask wereanalyzed by gas chromatography at different time intervals ranging from1 to 5 hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b from 49 to 71% and 8 to 16% wereobtained.

EXAMPLE 5

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt (nitrate, chloride oracetate) of praseodymium for 6 hours. Then the catalysts was filtered,washed with hot distilled water till the filtrated became anion free anddried overnight at 110° C. for removing the moisture. Clay catalysts,Pr-clay thus obtained was activated at 120° C. for 4 to 6 hours beforeusing for reaction. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 grams catalysts in abut 50 mlcapacity of round bottom flask kept in oil bath and the temperature ofoil bath was slowly raised to desired temperature of 100° C. The roundbottom flask provided with a water-circulator, temperature-controller,magnetic stirrer and moisture trap. The contents of the flask wereanalyzed by gas chromatography at different time intervals ranging from1 to 5 hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b from 23 to 62% and 12 to 39% wereobtained.

EXAMPLE 6

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt (nitrate, chloride oracetate) of samarium for 6 hours. Then the catalysts was filtered,washed with hot distilled water till the filtrated became anion free anddried overnight at 110° C. for removing the moisture. Clay catalysts,Sm-clay thus obtained was activated at 120° C. for 4 to 6 hours beforeusing for reaction. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 grams catalysts in abut 50 mlcapacity of round bottom flask kept in oil bath and the temperature ofoil bath was slowly raised to desired temperature of 100° C. The roundbottom flask provided with a water-circulator, temperature-controller,magnetic stirrer and moisture trap. The contents of the flask wereanalyzed by gas chromatography at different time intervals ranging from1 to 4 hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b from 56 to 63% and 6 to 39% wereobtained

EXAMPLE 7

Clay catalysts used in Example-3 was regenerated by washing with a polarsolvent like acetone and heated at 120 for 4 hours and reused foracylation of veratrole as described in example-3. Percent yield ofveratrole after first and second regeneration cycle were 80% and 75%respectively.

EXAMPLE 8

10 grams of H-clay prepared as described in Example-1 was refluxed with100 ml of the 0.01 M solution of soluble salt like nitrate, chloride oracetate of lanthanum for 6 hours. Then the catalysts was filtered,washed with hot distilled water till the filtrated became anion free anddried overnight at 110° C. for removing the moisture. Clay catalysts,La-clay thus obtained was activated at 120 ° C. for 4 to 6 hours beforeusing for reaction. 40 milimoles of aromatic ether and 40 milimoles ofacetic anhydride were reacted with 2 grams catalysts in about 50 mlcapacity of round bottom flask kept in oil bath and the temperature ofoil bath was slowly raised to desired temperature of 80° C. The roundbottom flask provided with a water-circulator, temperature-controller,magnetic stirrer and moisture trap. The contents of the flask wereanalyzed by gas chromatography at different time intervals ranging from1 to 4 hours. The percent yield of p-acyl veratrole and p-acyl anisolerespectively shown in table 1a and 1b from 29 to 40% and 15 to 30% wereobtained.

TABLE 1a Percent yields of p-acyl veratrole obtained on acylation ofveratrole using different catalysts. Ex. Yield of3,4-Dimethoxyacetophenone(%) No. Catalyst 1 hr 2 hr 3 hr 4 hr 5 hr 6 hr7 hr 8 hr 9 hr 1 H-Clay 31 59 52 58 65 69 72 77 69 2 La-Clay 56 68 86 8878 — — — — 3 Ce-Clay 57 69 75 91 85 — — — — 4 Nd-Clay 49 52 59 71 68 — —— — 5 Pr-Clay 23 42 55 62 58 — — — — 6 Sm-Clay 56 57 63 59 — — — — — 8La-Clay 29 33 38 40 37 — — — —

TABLE 1b Percent yields of p-acyl anisole obtained on acylation ofanisole using different catalysts. Yield of P-methoxyacetophenone(%)Ex..No. Catalysts 1 hr 2 hr 3 hr 4 hr 5 hr 6 hr 7 hr 1 H-Clay 12 13 1519 41 33 30 2 La-Clay 38 40 42 59 49 — — 3 Ce-Clay 35 42 59 62 58 — — 4Nd-Clay 8 12 14 16 14 — — 5 Pr-Clay 12 14 31 36 39 37 — 6 Sm-Clay 6 2339 32 — — — 8 La-Clay 15 19 24 30 27 — —

The mail advantages of the present invention are:

1. Acylation is done without use of any solvent, i.e., it is solventfree single step reaction.

2. High atom utilization and low mass ratio of waste to desired product(E-factor) for these conversion reflecting the environmentally friendlyproduction of p-acylated aromatic ether. Atom utilization is calculatedby dividing the molecular weight of the desired product by the sum ofthe all substances produced in the stochiometric equation, i.e. if weconsider the acylation of the anisole and veratrole by acetic anhydrideby using clay, reactions are represented as under.

Therefore in this reaction atom utilization is 151/210=71% for theacylation of anisole and 180/240=75% for the acylation of veratrole.E-factor is defined by the mass ratio of waste to desired product. Inthis reaction E-factor will be 60/151=0.4 for the acylation for anisoleand 60/80=0.33 for the acylation of veratrole.

3. Catalyst being solid in nature can be easily separated the reactionmixture by filtration or centrifuge. Clay can be regenerated up tosecond cycle and re-used.

4 Shape selectivity towards para selectivity is observed in very highyield values for the products,

5 Clay based catalysts are easy in handling in comparison conventionalFriedel-Craft acylation catalysts like H₂SO₄, HF, AlCl₃ and other Lewisacid.

6 Process uses inexpensive clay as a starting material for catalystpreparation.

We claim:
 1. A process for the preparation of an acylated aromatic etherwhich comprises acylating the aromatic ether with an acylating agent inthe presence of a solid acid heterogeneous catalyst comprising a rareearth cation exchanged clay based catalyst, the process being carriedout at an ether to catalyst ratio in the range of 1:5, separating thecatalyst and the acylated aromatic ether obtained.
 2. A process asclaimed in claim 1 wherein the lanthanide cation exchanged clay catalystis an upgraded smectite clay wherein the hydrogen ion is exchanged witha sodium ion.
 3. A process as claimed in claim 2 wherein the hydrogenion is exchanged with a sodium ion using an acid selected from the groupconsisting of HCl, HNO₃, and an organic acid.
 4. A process as claimed inclaim 1 wherein the rare earth ion is selected from the group consistingof lanthanum, cerium, neodymium, praseodymium and samarium.
 5. A processas claimed in claim 4 wherein the amount of rare earth ion in thecatalyst is in the range of 5 to 10 weight % of the clay.
 6. A processas claimed in claim 4 wherein the rare earth ion is obtained using asoluble salt of the rare earth selected from the group consisting ofnitrate, chloride and acetate.
 7. A process as claimed in claim 1wherein the acylation of the aromatic ether is carried out in a singlestep under solvent free condition and at a temperature in the range of80 to 120° C. and under atmospheric conditions without generating anyby-product.
 8. A process as claimed in claim 7 wherein the acylation ofthe aromatic ether is carried out at a temperature of 100° C.
 9. Aprocess as claimed in claim 1, wherein the acylating agent is selectedfrom the group consisting of a chloride and a carboxylic acid anhydride.10. A process as claimed in claim 8 wherein the carboxylic acidanhydride is acetic acid anhydride or a homologue thereof.
 11. A processas claimed in claim 1 wherein the catalyst is separated and recycled.12. A process as claimed in claim 1 wherein the aromatic ether isselected from the group consisting of veratrole and anisole.
 13. Aprocess as claimed in claim 1 wherein the process is solvent free withthe aromatic ether itself acting as the solvent.
 14. A process asclaimed in claim 1 wherein the catalytic reaction is carried out at apressure in the range from 1 to 20 atmospheres.
 15. A process as claimedin claim 1 wherein the ether to catalyst ratio is in the range of 1:3 to1:5.
 16. A clay based catalytic process for the preparation of anacylated aromatic ether which comprises (i) preparing upgraded smectiteclay in the range of 0.5 to 5% weight percent; (ii) drying the clay inthe temperature of 80 to 120° C. for 8 to 12 hours; (iii)exchanginghydrogen ion for sodium ion using a mineral acid selected from the groupconsisting of HCl and HNO₃ or an organic acid; (iv) preparing Lanthanideexchanged clay using a soluble salt of a lanthanide cation; (v)maintaining the ether to catalyst ratio in the range of 1 to 5; mixingthe catalyst so prepared with the aromatic ether and an acylating agentand acylating the aromatic ether at a reaction temperature in the rangeof 80 to 120° C. and time in the range of 1 to 9 hours under solventfree reaction mixture at atmospheric pressure; (vi) separating thecatalyst and the acylated product by distillation.